Another SDF official, Redur Xelil, said commanders hope to capture the IS territory by the end of February, but warned that the terror group would continue to pose "great and serious" security threats afterwards.

Image:More than 20,000 civilians have been evacuated in the last 10 days

The United States has echoed that comment, pointing out that IS retains leaders, fighters, facilitators and resources that could fuel an insurgency.

Donald Trump has said he expects an announcement as soon as Wednesday that the area has been reclaimed.

The US president announced in December that he was withdrawing all 2,000 US troops from Syria because the fight against IS was almost won.

That move is expected by the end of April, the Wall Street Journal reported on Friday - a date also confirmed to Reuters.